1. Field of the Invention
The disclosures herein relate to a developing device, an image forming apparatus and an image forming method for developing an image in a hopping developing system by attaching a toner hopping on a surface of a toner carrier to a latent image formed on a latent image carrier.
2. Description of the Related Art
Japanese Patent Application Publication No. 2008-008929 (hereinafter called “Patent Document 1”) discloses one example of an image forming apparatus configured to develop an image in a hopping developing system. The disclosed image forming apparatus includes a developing device that includes a toner carrier roller formed of a rotatable cylindrical base and two or more electrodes adjacently arranged at a predetermined pitch along a periphery of the cylindrical base. In the image forming apparatus, a first periodic pulse voltage and a second periodic pulse voltage respective phases of which are shifted from each other are applied to adjacent electrodes. When such first and second periodic pulse voltages having mutually shifted phases are applied to the adjacent electrodes, alternating fields are formed between the adjacent electrodes, which cause toner on a surface of a toner carrier roller to reciprocate between the adjacent electrodes while exhibiting a hopping behavior. The toner is thus carried to a developing region formed between the toner carrier roller and the photoreceptor where the toner carrier faces a photoreceptor with a rotational movement of the toner carrier roller while reciprocally hopping between the adjacent electrodes. In the developing region, the toner hopping on the surface of the toner carrier is attracted to an electrostatic latent image formed on the photoreceptor. The attracted toner is attached to the electrostatic latent image of the photoreceptor, which is thus developed to form a toner image.
In such a hopping developing system where the electrostatic latent image is developed by attaching the hopping toner to the electrostatic latent image, it may be possible to implement a low voltage development due to an extremely small potential difference between the electrostatic latent image and a bare surface exposed around the electrostatic latent image of the photoreceptor. Further, in the hopping developing system, the potential difference between the electrostatic latent image and the bare surface may be reduced approximately several tens μV, which may not be realized by a one-component developing system in which the development is carried out by utilizing toner attached to a surface of a developing roller, or a two-component developing system where the development is carried out by utilizing toner attached to carrier particles carried on a surface of the developing roller. Thus, the reduction in the potential difference may reduce the load caused by the potential difference on the surface of the photoreceptor to elongate the life of the photoreceptor.
In the hopping developing system, in order to stabilize the amount of toner transferred to the developing region, there is proposed a developing device that is provided with a regulator blade to regulate a thickness of a toner layer on the surface of the toner carrier roller. In this developing device, the amount of toner transferred to the developing region is regulated by bringing the regulator blade into contact with the surface of the toner carrier roller before entering into the developing region. Further, in the development device having the above configuration, the toner layer may be regulated to a certain thickness by applying a direct (DC) voltage having a polarity the same as the polarity of toner charge to the regulator blade.
However, the related art image forming apparatus having the hopping developing system only includes a power supply to generate the above-described periodic pulse voltages as a power supply to generate bias applied to various components and members of the developing device. However, if the image forming apparatus having the hopping developing system is further provided with a direct-current (DC) power supply in addition to the above power supply to generate a periodic pulse voltage, the cost may be increased.